Urea-water pump device

ABSTRACT

A urea-water pump device for an exhaust gas cleaner includes a pump, a motor, a temperature detection portion, a setting portion, and a changing portion. The pump is accommodated in a tank and supplies urea-water stored in the tank. The motor drives the pump. The temperature detection portion directly or indirectly detects a temperature of the urea-water stored in the tank. The setting portion sets an upper-limit-value of a current supplied to the motor. The changing portion changes the upper-limit-value of the current supplied to the motor, based on the temperature of the urea-water detected by the temperature detection portion.

CROSS-REFERENCE TO RELATED APPLICATION

The application is based on Japanese Patent Application No. 2012-16578 filed on Jan. 30, 2012, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a urea-water pump device for an exhaust gas cleaner.

BACKGROUND

Conventionally, a urea selective catalyst reduction (SCR) system is publicly known for reducing nitrogen oxide (NOx) included in gas exhausted from an internal combustion engine by adding urea-water. In a urea SCR system described in JP-2009-144644A, urea-water stored in a tank is supplied to an injector provided in an exhaust passage by a pump accommodated in the tank. When the urea-water is frozen in a low temperature environment, the urea-water is thawed by heat generated by a motor of the pump which is activated. In a view of protecting the motor and a control circuit for the motor, it is necessary to control a current supplied to the motor at the startup time.

When the current supplied to the motor is constricted during the startup time, a heat-generation amount of the motor may decrease, because the heat-generation amount is proportional to the supplied current. In this case, the heat-generation amount may be not enough for thawing the urea-water in the tank.

SUMMARY

It is an object of the present disclosure to provide a urea-water pump device so that thawing of urea-water can be promoted and that protection of a motor and a control circuit can be achieved.

According to an aspect of the present disclosure, an exhaust gas cleaner cleans exhaust gas by adding a urea-water stored in a tank to the exhaust gas flowing though an exhaust passage, and a urea-water pump device for the exhaust gas cleaner includes a pump, a motor, a temperature detection portion, a setting portion, and a changing portion. The pump is accommodated in the tank, and supplies the urea-water stored in the tank toward the exhaust passage. The motor drives the pump. The temperature detection portion directly or indirectly detects a temperature of the urea-water stored in the tank. The setting portion sets an upper-limit-value of current supplied to the motor. The changing portion changes the upper-limit-value of the current supplied to the motor, based on the temperature of the urea-water detected by the temperature detection portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a block diagram illustrating an outline of a urea-water pump device according to a first embodiment;

FIG. 2 is a schematic view illustrating an outline of an exhaust gas cleaner having the urea-water pump device according to the first embodiment;

FIG. 3 is a flowchart illustrating a procedure performed by a controller of the urea-water pump device according to the first embodiment;

FIG. 4 is a graph illustrating a relationship between time and current supplied to a pump which discharges non-frozen urea-water;

FIG. 5 is a graph illustrating a relationship between time and current supplied, to a pump which discharges frozen urea-water, according to the first embodiment;

FIG. 6 is a graph illustrating a relationship between time and current supplied to a pump which discharges frozen urea-water, according to a comparison example; and

FIG. 7 is a block diagram illustrating an outline of a urea-water pump device according to a second embodiment,

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described hereafter referring to drawings. In the embodiments, a part that corresponds to a matter described in a preceding embodiment may be assigned with the same reference numeral, and redundant explanation for the part may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. The parts may be combined even if it is not explicitly described that the parts can be combined. The embodiments may be partially combined even if it is not explicitly described that the embodiments can be combined, provided there is no harm in the combination.

First Embodiment

An exhaust gas cleaner 10 having a urea-water pump controller 20 will be described referring to FIG. 2. The exhaust gas cleaner 10 may correspond to a urea-water selective catalytic reduction system (urea-water SCR system). In the urea-water SCR system, urea-water is added into exhaust gas which is exhausted from an internal combustion engine 11 mounted to a vehicle to reduce nitrogen oxide (NOx) included in the exhaust gas. The exhaust gas is exhausted to the atmosphere via an exhaust passage 13 defined by an exhaust pipe 12. The internal combustion engine 11 may be a diesel engine. The exhaust gas cleaner 10 is not limited to be applied to the diesel engine. The exhaust gas cleaner 10 may be applied to a gasoline engine or a gas turbine engine.

The exhaust gas cleaner 10 includes a tank 14, a pump 15, a urea-water pipe 16, and an injector 17. The tank 14 stores the urea-water (urea solution). The pump 15 is accommodated in the tank 14. At least a part of the pump 15 is immersed into the urea-water in the tank 14. The urea-water pipe 16 couples the pump 15 and the injector 17 with each other. The urea-water discharged from the pump 15 is supplied to the injector 17 via a urea-water passage 18 defined by the urea-water pipe 16. The injector 17 is provided in the exhaust pipe 12 which defines the exhaust passage 13. The injector 17 is inserted into the exhaust pipe 12. The injector 17 includes an injection port (not shown) on the end portion. The end portion of the injector 17 is exposed in the exhaust passage 13. The urea-water is injected from the injection port of the injector 17 into the exhaust gas flowing through the exhaust passage 13. A reduction catalyst 19 is provided in the exhaust passage 13. The exhaust gas and the urea-water are mixed in the exhaust passage 13, and then the mixture flows into the reduction catalyst 19. The NOx included in the exhaust gas is reduced in the reduction catalyst 19 by reacting with the urea-water. The urea-water may be added into the exhaust gas by other components instead of the injector 17.

The urea-water pump controller 20 includes a motor 21, a control unit 22, and a temperature sensor 23 in addition of the pump 15 of the exhaust gas cleaner 10. The motor 21 may be a DC brushless motor activated by a current supplied from the control unit 22. The motor 21 drives the pump 15. Thus, the pump 15 discharges the urea-water from the tank 14 to the urea-water passage 18 by an operation of the motor 21. The motor 21 is unified with the pump 15, and at least a part of the motor 21 is immersed into the urea-water in the tank 14 as the same with the pump 15. The temperature sensor 23 detects a temperature of the urea-water in the tank 14. The temperature sensor 23 transmits an electrical signal corresponding to the detected temperature of the urea-water to the control unit 22.

The urea-water pump controller 20 further includes a urea-water quantity sensor 24 and a heater 25. The urea-water quantity sensor 24 detects a quantity of the urea-water stored in the tank 14. The urea-water quantity sensor 24 transmits the detected quantity of the urea-water to the control unit 22 as an electrical signal. The heater 25 generates heat by an electrical power supplied from the control unit 22. The temperature of the urea-water is kept by the heat generated by the heater 25.

The control unit 22 will be described referring to FIG. 1. The control unit 22 includes a controller 31 configured by a microcomputer having a CPU, a ROM and a RAM (not shown). The controller 31 may correspond to a temperature acquiring portion 32, a changing portion 33, a setting portion 34, and a motor driver 35, as a hard ware by a unified electronic circuit. In addition, based on implementing a computer program stored in the ROM of the controller 31, the temperature acquiring portion 32, the changing portion 33, the setting portion 34, and the motor driver 35 may be achieved by a combination of a soft ware and a hard ware.

The temperature acquiring portion 32 is coupled to the temperature sensor 23, and acquires a detected temperature from the temperature sensor 23. According to the present embodiment, the temperature sensor 23 directly detects the temperature of the urea-water in the tank 14. In this case, the temperature sensor 23 and the temperature acquiring portion 32 may configure a temperature detection portion 36.

Further, the temperature detection portion 36 may also indirectly detect the temperature of the urea-water. An outside temperature, a coolant temperature of the internal combustion engine 11, or a temperature of an environment surrounding the control unit 22, relates to the temperature of the urea-water in the tank 14. In this case, the temperature of the urea-water may be indirectly measured based on at least one of the outside temperature detected by an outside sensor, the coolant temperature of the internal combustion engine 11 detected by a coolant sensor, and a temperature of the control unit 22 detected by a temperature sensor.

The changing portion 33 changes an upper-limit-value Ia for a current supplied to the motor 21. The current supplied to the motor 21 has a preset upper-limit-value for protecting elements of electronic circuits configuring the motor 21 and the control unit 22. The upper-limit-value Ia is set to an initial value Id as an inherent initial value of the motor 21 and the control unit 22. The changing portion 33 changes the upper-limit-value Ia based on a temperature of the urea-water detected by the temperature detection portion 36.

Specifically, when the temperature of the urea-water is smaller than or equal to a preset lower-limit-value 11, the changing portion 33 changes the upper-limit-value Ia to a value larger than the initial value Id. The lower-limit-value Ti corresponds to a melting point of the urea-water.

The setting portion 34 sets the upper-limit-value of the current supplied to the motor 21 to the upper-limit-value Ia changed by the changing portion 33. The motor driver 35 is coupled to the motor 21. The motor driver 35 controls the motor 21 according to a load of the pump 15 under a condition with the upper-limit-value Ia set by the setting portion 34.

Since at least a part of the motor 21 is immersed in the urea-water in the tank 14 as the same with the pump 15, the temperature of the motor 21 relates to the temperature of the urea-water in the tank 14. The motor 21 generates heat by a current supplied from the control unit 22 for activating the motor 21. When the temperature of the urea-water surrounding the motor 21 is low, the raising in the temperature of the motor 21 is slight because the heat generated by the motor 21 is absorbed by the urea-water even though the current supplied to the motor 21 has a relatively large value. When the temperature of the urea-water surrounding the motor 21 is high, the temperature of the motor 21 may raise easily. Therefore, the upper-limit-value Ia can be set larger when the temperature of the urea-water is low.

The changing portion 33 changes the upper-limit-value la based on the temperature of the urea-water detected in the temperature detection portion 36. Specifically, when the temperature of the urea-water is smaller than or equal to the preset lower-limit-value Ti, the changing portion 33 changes the upper-limit-value Ia to a value larger than the initial value Id. The setting portion 34 sets the upper-limit-value of the current supplied to the motor 21 to the upper-limit-value changed by the changing portion 33. Therefore, a current value larger than the initial value Id is supplied from the motor driver 35 to the motor 21.

Operation of the urea-water pump controller 20 will be described with reference to FIG. 3.

At S101, the setting portion 34 sets the upper-limit-value to the initial value Id when an engine control unit (ECU, not shown) of the internal combustion engine 11 requires to activate the pump 15. That is, the setting portion 34 sets the upper-limit-value to the inherent initial value Id for safety. Thus, the current supplied to the motor 21 is controlled up to the initial value Id at first.

At S102, the temperature detection portion 36 detects the temperature of the urea-water in the tank 14 from the temperature sensor 23 and the temperature acquiring portion 32.

At S103, the changing portion 33 determines whether the temperature of the urea-water detected at S102 is smaller than or equal to the preset lower-limit-value Ti. Because the melting point of the urea-water varies according to the concentration of the urea in the urea solution, the lower-limit-value Ti is set according to the concentration of the urea.

When the temperature of the urea-water is smaller than or equal to the lower-limit-value Ti (S103: Yes), the initial value Id set at S101 is changed at S104. That is, the changing portion 33 cancels the initial value Id, and changes the upper-limit-value to infinity (unlimited) at S104. Alternatively, the changing portion 33 may change the upper-limit-value to an extended upper-limit-value Ib which is preset according to the initial value Id. The extended upper-limit-value Ib may be larger than the initial value Id. The extended upper-limit-value Ib is set as an optional value such that the motor 21 and the control unit 22 are not damaged. Furthermore, the changing portion 33 may change the upper-limit-value by using a function with respect to the temperature of the urea-water. Thus, the changing portion 33 changes the upper-limit-value to a value larger than the initial value Id according to the temperature detected at S102.

The setting portion 34 sets the upper-limit-value Ia, which is changed at S104. When the temperature of the urea-water is smaller than or equal to the lower-limit-value Ti which corresponds to the melting point of the urea-water, the urea-water may freeze. The generation of heat in the motor 21 is used for thawing the urea-water even though the upper-limit-value Ia is changed to a value larger than the initial value Id. An increase in the temperature of the motor 21 is constricted by the thawing. Therefore, since the setting portion 34 sets the upper-limit-value Ia to a value larger than the initial value Id, a thawing of the urea-water is promoted while the motor 21 is protected.

After the upper-limit-value Ia is changed at S104, the motor 21 is activated at S105. That is, the motor driver 35 supplies a current to the motor 21 in a manner that the upper-limit-value of the current corresponds to the upper-limit-value Ta changed at S104.

When the temperature of the urea-water is larger than the lower-limit-value Ti (S103: No), the changing portion 33 keeps the upper-limit-value Ta to the initial value Id set at S101. In this case, the motor driver 35 activates the motor 21 in a manner that the upper-limit-value of the current supplied to the motor 21 is set to the initial value Id which is set at S101.

When the motor 21 is activated, the controller 31 determines whether a stop request for requesting a stop of the pump 15 is transmitted from the ECU, at S106. When the controller 31 received the stop request (S106: Yes), the controller 31 stops the motor 21 at S107. Then the procedure is completed.

When the controller 31 determines that no stop request is received (S106: No), the temperature detection portion 36 detects the temperature of the urea-water once again at S108. Then, at S109, the changing portion 33 determines whether the temperature of the urea-water detected at S108 is larger than the preset lower-limit-value Ti.

When the changing portion 33 determines that the temperature of the urea-water detected at S108 is larger than the lower-limit-value Ti (S109: Yes), the changing portion 33 changes the upper-limit-value Ia changed at S104 to the initial value Id again at S110.

When the temperature of the urea-water is larger than the lower-limit-value Ti, it is likely that the urea-water has thawed completely. Thus, a urea-water quantity of absorbing the generation of heat in the motor 21 decreases. If the upper-limit-value of the current supplied to the motor 21 is kept to a value larger than the initial value Id, the motor 21 may overheat, and then elements of the motor 21 and the motor driver 35 may be damaged. In this case, it is necessary that the changing portion 33 changes the upper-limit-value Ta changed at S104 to the initial value Id again.

When the upper-limit-value Ia is changed to the initial value Id again at S110, the controller 31 returns to S106. When the changing portion 33 determines that the temperature of the urea-water is smaller than or equal to the lower-limit-value Ti (S109: No), the changing portion 33 keeps the upper-limit-value Ta changed at S104. That is, the changing portion 33 repeats the routine without changing the upper-limit-value. When the temperature of the urea-water is smaller than or equal to the lower-limit-value Ti, it is likely that the urea-water has not thawed yet. Therefore, the changing portion 33 keeps the upper-limit-value to the upper-limit-value Ia changed at S104.

FIG. 4 illustrates a case where non-frozen urea-water is discharged from the pump 15 to the injector 17. In this case, the current supplied to the motor 21 increases in accordance with a startup of the motor 21. The current flowing through the motor 21 becomes the maximum directly after the motor 21 is activated as a startup current Is. Usually, the upper-limit-value is set to the initial value Id for protecting the elements of the motor 21 and the motor driver 35. Thus, the current reaches the initial value Id before reaching the startup current Is, so the current is limited to the initial value Id. When the motor 21 operates continuously, a load of the pump 15 decreases, and thereby the value of the current becomes smaller than the initial value Id. The motor 21 can operate stably according to the current smaller than the initial value Id.

FIG. 5 illustrates a case where frozen urea-water is discharged from the pump 15 to the injector 17 according to the first embodiment. In the first embodiment, the upper-limit-value Ia is changed to a value larger than the initial value Id. Then, the current supplied to the motor 21 reaches the startup current Is larger than the initial value Id.

After the motor 21 is activated, the current supplied to the motor 21 is lowered to become smaller than the startup current Is in accordance with time. At this time, the current is kept to an operation current Ir which is larger than the initial value Id by a load applied to the pump 15 from the frozen urea-water.

According to the first embodiment, since the upper-limit-value Ia is changed to a value larger than the initial value Id, the operation current Ir supplied to the motor 21 is kept as the value larger than the initial value Id. When the urea-water is frozen, a current larger than the initial value Id is continuously supplied to the motor 21. Thus, the generation of heat in the motor 21 becomes larger, and the thawing of the urea-water in the tank 14 is promoted. Since the urea-water is frozen, the generation of heat in the motor 21 is used for thawing the urea-water.

After the urea-water is thawed, the temperature of the urea-water increases so that the temperature becomes larger than the lower-limit-value Ti (melting point). When the temperature of the urea-water is larger than the melting point, the upper-limit-value Ia is changed to the initial value Id. Then, the current supplied to the motor 21 is smaller than or equal to the initial value Id. Thus, the generation of heat in the motor 21 decreases.

A comparison example will be described with reference to FIG. 6 in which the current supplied to the motor 21 is limited to the initial value Id. When the frozen urea-water is discharged from the pump 15 to the injector 17, the upper-limit-value Ia is kept to the initial value Id. The current supplied to the motor 21 is limited to the initial value Id even during the startup of motor 21. Besides, the current supplied to the motor 21 is kept to the initial value Id after the motor 21 is activated even when a load is added to the pump 15 by the frozen urea-water.

In the comparison example, the current value corresponding to the initial value Id is supplied to the motor 21, no matter whether the urea-water is frozen. If a size of the motor 21 or the control unit 22 is relatively smaller, the rated temperature is low. In this case, if the upper-limit-value cannot be set to be a value larger than the initial value Id, the generation of heat in the motor 21 may not be enough so that it is difficult to thaw the urea-water by the generation of heat.

In FIG. 5, the current supplied to the motor 21 is increased by a hatched area with diagonal lines, according to the first embodiment, with respect to the comparison example shown in FIG. 6. A heat-generation amount of the motor 21 is proportional to the supplied current. Thus, the heat-generation amount of the first embodiment is larger than the heat-generation amount of the comparison example. The thawing of the frozen urea-water is promoted in the first embodiment.

Usually, a startup time limit-value of the current supplied to the motor is set according to the motor and a controller for controlling the motor. Specifically, the startup time limit-value of the current flowing through the motor is set to a specified value in a manner that the temperatures of the motor and the controller are not exceeding the rated temperature when the motor and the controller are used in the highest temperature environment allowed for the motor and the controller.

Temperatures of the pump and the motor are substantially the same as the temperature of the urea-water, so the motor is in a sufficiently low temperature environment where the urea-water is frozen. A controller for controlling the motor, such as a changing portion or a setting portion, is most likely in the sufficiently low temperature environment. In this case, an increase in the temperature of the motor and the controller is constricted according to the low temperature environment, even though the motor is activated. Therefore, when a current larger than usual is supplied to the motor, a heat-generation amount of the motor is ensured, while the increase in the temperatures of the motor and the control circuit are constricted.

The limit-value is set to a specified value within a range in which the temperatures of the motor and the control circuit are not exceeding the rated temperature, even in the highest temperature environment. When the motor is activated in the low temperature environment, the temperatures of the motor and the controller are kept to a temperature sufficiently lower than the rated temperature even though the current corresponding to the limit-value is supplied. Thus, the limit-value can be set to a value larger than usual, and the current having the value can be supplied to the motor, when the motor and the control circuit are in the low temperature environment.

According to the first embodiment, the changing portion 33 changes the upper-limit-value of the current supplied to the motor 21 based on the temperature of the urea-water of the tank 14 detected by the temperature detection portion 36. The temperatures of the pump 15 and the motor 21 are substantially the same as the temperature of the urea-water. When the urea-water is frozen, not only the motor 21, but also the control unit 22 such as the changing portion 33 or the setting portion 34 are in a sufficiently low temperature environment. In this case, an increase in the temperature of the motor 21 or the control unit 22 is constricted according to the low temperature environment, even when a relatively-large current flows through the motor 21. When a current larger than usual is supplied to the motor 21, the heat-generation amount of the motor 21 is ensured, while the increase in the temperatures of the motor 21 and the control unit 22 are constricted.

When the changing portion 33 changes the upper-limit-value Ia based on the temperature of the urea-water, the setting portion 34 sets the current supplied to the motor 21 to the upper-limit-value Ia changed by the changing portion 33. Since the current larger than the initial value Id is supplied to the motor 21 in the low temperature environment, the heat-generation amount of the motor 21 increases. Therefore, a large heat-generation amount can be obtained even when the size of the motor 21 or the control unit 22 is small, in which the rated temperature is low.

Thus, a protection of the motor 21 or the control unit 22 can be achieved, and the thawing of the urea-water can be promoted. The motor 21 can be used together with the heater 25 for thawing the urea-water by using the generation of heat in the motor 21. In this case, if a thawing time is fixed, an output of the heater 25 and the power consumption can be reduced. Further, if the output of the heater 25 is maintained, the thawing can be rapidly achieved.

According to the first embodiment, the changing portion 33 sets the upper-limit-value Ia to the inherent initial value Id when the temperature of the urea-water is larger than the lower-limit-value Ti. That is, the changing portion 33 sets the upper-limit-value Ia to the initial value Id when the temperature of the urea-water is larger than the melting point. When the temperature of the urea-water surrounding the motor 21 increases, the upper-limit-value of the current supplied to the motor 21 is reset to the inherent initial value Id. Therefore, the protection of the motor 21 or the control unit 22 can be achieved.

Second Embodiment

The urea-water pump controller 20 according to a second embodiment is shown in FIG. 7.

The urea-water pump controller 20 according to the second embodiment further includes a timer 41 as a time detection portion compared with the first embodiment. The timer 41 detects an elapsed time period from a point that the motor 21 is activated. The changing portion 33 changes the upper-limit-value Ia to the inherent initial value Id of the motor 21, when the elapsed time period detected by the timer 41 is larger than a preset setting time period.

The changing portion 33 changes the upper-limit-value Ia to the initial value Id when the temperature of the urea-water is larger than the lower-limit-value Ti (melting point) in the first embodiment.

In contrast, in the second embodiment, the current supplied to the motor 21 may be controlled by a supplying time instead of the temperature of the urea-water, in a view of protecting the motor 21. The supplying time is an elapsed time period where the current supplied to the motor 21 is larger than the initial value Id. Therefore, according to the second embodiment, the timer 41 detects the elapsed time period from a point that the motor 21 is activated. When the elapsed time period is larger than the preset setting time period, the changing portion 33 changes the upper-limit-value Ia to the initial value Id. In the second embodiment, the elapsed time period is controlled to be within the setting time period.

According to the second embodiment, the changing portion 33 changes the upper-limit-value Ia to the inherent initial value Id of the motor 21, when the elapsed time period is larger than the setting time period. A time period, in which the current larger than the initial value Id is supplied to the motor 21, is controlled to be within the setting time period. Thus, an electronic circuit of the motor 21 or the control unit 22 can be protected.

Such changes and modifications are to be understood as being within the scope of the present disclosure as defined by the appended claims. 

What is claimed is:
 1. A urea-water pump device for an exhaust gas cleaner cleaning exhaust gas by adding a urea-water stored in a tank to the exhaust gas flowing through an exhaust passage, the urea-water pump device comprising: a pump accommodated in the tank, the pump supplying the urea-water from the tank toward the exhaust passage; a motor driving the pump; a temperature detection portion directly or indirectly detecting a temperature of the urea-water stored in the tank; a setting portion setting an upper-limit-value of a current supplied to the motor; and a changing portion changing the upper-limit-value of the current supplied to the motor based on the temperature of the urea-water detected by the temperature detection portion.
 2. The urea-water pump device according to claim 1, wherein the changing portion changes the upper-limit-value to a value larger than a preset inherent initial value when the temperature of the urea-water detected by the temperature detection portion is smaller than or equal to a preset lower-limit-value.
 3. The urea-water pump device according to claim 1, wherein the changing portion changes the upper-limit-value to a preset inherent initial value when the temperature of the urea-water detected by the temperature detection portion is larger than a preset lower-limit-value.
 4. The urea-water pump device according to claim 1, wherein the changing portion further has a time detection portion detecting an elapsed time period from a point that the motor is activated, and the changing portion changes the upper-limit-value to a preset inherent initial value when the elapsed time period detected by the time detection portion is larger than a preset setting time period. 